The present invention relates to a rotary electric machine, and more particularly to a rotary electric machine including a centrifugal cooling fan which is used as, for example, an electric motor and a power generator mounted on vehicles.
Heretofore, there has been known a rotary electric mahine comprising a housing having front and rear end walls, a rotary shaft operatively connected with a driving pulley and rotatably supported by the housing, and a cooling fan having on its periphery a plurality of or a series of fan blades. The end walls of the housing is formed therein with a plurality of air vents for producing an air circulation through the housing during rotation of the cooling fan, so as to cool heated parts such as a stator and a rotor housed in the housing. The cooling fan includs a disc-shaped metal plate having on its periphery a plurality of substantially radially extending and circumferentially spaced fan blades each formed by bending a radially outer portion of the metal plate upstandingly with respect to the surface of the metal plate. Further, with the structure of the cooling fan described, a plurality of notches are defined between the adjacent fan blades. In other words, the cooling fan has on its periphery the plurality of fan blades and notches alternately in a zigzag fashion. However, during rotation of the cooling fan of the structure described, there occurs an air flow passing through the notches oppositely to an ordinary air flow passing through the housing, which makes the cooling efficiency inferior and causes large noises.
In order to cope with the above problem, it has been proposed to attach by spot welding or the like a backing disc-plate on a back surface of the cooling fan, or the surface of the cooling fan opposite to the fan blades, in a manner to block or cover therewith the notches and thus preventing an air from passing therethrough. However, according to a series of experiments conducted by the inventors, it was found that the cooling fan thus improved suffered from a disadvantage such that there produced rattling noises by occasional vibratory contact between the cooling fan and the disc plate, particularly during an abrupt acceleration or deceleration of vehicles on which the rotary electric machine is moutned. The rattling noises are considered to occur due to a close face-to-face location of the disc-plate and the cooling fan, since it is technically difficult to attach the disc-plate on the back surface of the cooling fan in a uniformly contacted manner.
Also the improved cooling fan described suffered from an increased production cost, since the disc-plate, which is an additional member of the cooling fan, must be securely attached onto the cooling fan before it is assembled in the rotary electric machine.